Method and apparatus for storing data using spin-polarized electrons

ABSTRACT

A data storage device including a substrate, a data storage layer on the substrate, and a spin-polarized electron source. The data storage layer comprises a fixed number of atomic layers of a magnetic material which provide the data storage layer with a magnetic anisotropy perpendicular to a surface of the data storage layer. A data magnetic field is created in the data storage layer. The data magnetic field is polarized either in a first direction corresponding to a first data value or in a second direction corresponding to a second data value. Data is stored in the data storage layer by providing a spin-polarized electron having an electron magnetic field with a direction of polarization corresponding to one of the first and the second data values, the electron having a wavelength &#34;characteristic&#34; of unpaired electrons in the data storage layer which cause the magnetic moment of the material, and directing the spin-polarized electron at the data magnetic field to impart the direction of polarization of the electron magnetic field to the data magnetic field. Data is read from the data storage layer by directing the spin-polarized electron at a second wavelength at the data magnetic field and detecting a deflection or attraction of the spin-polarized electron by the data magnetic field. Alternatively, data is read from the data storage layer by directing the spin-polarized electron at the data magnetic field so that the magnetic medium produces a secondary electron and then detecting certain characteristics of the secondary electron.

This application is a division of Ser. No. 08/641,418 filed May 1, 1996now U.S. Pat. No. 5,838,020 which is a continuation of Ser. No.08/311,738 filed Sep. 23, 1994 now U.S. Pat. No. 5,546,337 which is acontinuation-in-part of U.S. application of Thomas D. Hurt and Scott A.Halpine for DATA STORAGE MEDIUM FOR STORING DATA AS A POLARIZATION OF ADATA MAGNETIC FIELD AND METHOD AND APPARATUS USING SPIN-POLARIZEDELECTRONS FOR STORING THE DATA ONTO THE DATA STORAGE MEDIUM AND READINGTHE STORED DATA THEREFROM, filed Jan. 31, 1994, Ser. No. 08/188,828,U.S. Pat. No. 5,446,687 the contents of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to data storage and retrieval. Moreparticularly, the present invention relates to a data storage medium anda method and apparatus for storing data onto the data storage medium andreading the stored data therefrom.

2. Description of the Related Art

Over the years, there has been an increasing need for high speed massdata storage devices. With the conversion from analog systems to digitalsystems and the increasing speed of processing demonstrated by currentprocessor technology, the ability to quickly access large amounts ofdata is lagging behind demand. This is especially true in the scientificworld for computer modeling and simulations, as well as in the consumerworld for high definition television (HDTV), HDTV video records, compactdisks, personal digital assistants (PDAs), personal communicationassistants (PCAs), digital tape decks, and even such items asautomobiles. Furthermore, the merging worlds of computers, multimedia,and communication will impact consumers through virtual reality,interactive television, voice recognition systems (vocally interactive),handwriting recognition systems, and integrated communications withentertainment systems, each of which will require high speed nonvolatilemass data storage.

Applying conventional lithographic techniques and incrementalimprovement processes to current memory technologies has resulted inincremental progress. This incremental progress will simply exacerbatethe disparity between the increasing speed of processors and theircapability to store and effectively utilize needed amounts of data.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a data storage mediumand a method and apparatus for storing data onto the data storage mediumand reading the stored data therefrom that substantially obviates one ormore of the problems due to the limitations and disadvantages of therelated art.

Features and advantages of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the method and apparatus particularly pointed out in thewritten description and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described, a data storagedevice comprises a member including a magnetic material; means forgenerating a beam of electrons, the beam electrons having a commonmagnetic polarization in one of a first direction and a seconddirection, the beam being directable at one of a plurality of portionsof the member; means, responsive to an address signal, for directing thebeam to a portion of the member corresponding to the address signal, andfor controlling the wavelength of the beam electrons such that theportion of the member assumes a magnetic polarization corresponding tothe magnetic polarization of the beam electrons; and means, responsiveto the address signal, for detecting the polarization of a portion ofthe member corresponding to the address signal, by directing the beam atthe portion.

According to another aspect of the invention, a method of operating asystem including a member having a magnetic material, and a means forgenerating a beam of electrons, the beam electrons having a commonmagnetic polarization in one of a first direction and a seconddirection, the beam being directable at one of a plurality of portionsof the member, the method comprises the steps of receiving an addresssignal; directing the beam to a portion of the member corresponding tothe address signal and controlling the wavelength of the beam electronssuch that the portion of the member assumes a magnetic polarizationcorresponding to the magnetic polarization of the beam electrons.

According to another aspect of the invention, a method of operating asystem including a member having a magnetic material, and a means forgenerating a beam of electrons, the beam electrons having a commonmagnetic polarization in one of a first direction and a seconddirection, the beam being directable at one of a plurality of portionsof the member, the method comprises the steps of receiving an addresssignal; directing the beam to a portion of the member corresponding tothe address signal and controlling the wavelength of the beam electronssuch that the portion of the member assumes a magnetic polarizationcorresponding to the magnetic polarization of the beam electrons; andsubsequently, detecting the polarization of a portion of the membercorresponding to the address signal, by directing the beam at theportion.

According to another aspect of the invention, a method of storing dataas a direction of polarization in a magnetic material, the methodcomprises the steps of providing a spin-polarized electron having anelectron magnetic field, the electron magnetic field having a directionof polarization corresponding to one of first and second data values,the electron having a wavelength characteristic of unpaired electronsthat cause the magnetic moment of the magnetic material; and directingthe spin-polarized electron, through an electrically nonconductiveenvironment, at a portion of the magnetic material to impart thedirection of polarization of the electron magnetic field to the portion.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate a presently preferred embodimentof the invention and, together with the description, serve to explainthe principles of the invention. In the drawings:

FIG. 1 is a cross-sectional view of data storage and retrieval device ofthe preferred embodiment of the present invention;

FIG. 2 is plan view of a stigmator element for use in the data storageand retrieval device of FIG. 1;

FIGS. 3(a) and 3(b) are partial cross-sectional views of the datastorage medium of FIG. 1;

FIG. 4(a) is a plan view of the data storage medium of FIG. 1;

FIG. 4(b) is a partial cross-sectional view of the data storage mediumof FIG. 1 showing parking and alignment areas;

FIGS. 5(a)-5(b) are partial cross-sectional views of the data storagemedium of FIG. 1 during a data store operation;

FIGS. 6(a)-6(b) are partial cross-sectional views of the data storagemedium of FIG. 1 during a first data read operation;

FIGS. 7(a)-7(b) are partial cross-sectional views of the data storagemedium of FIG. 1 during a second data read operation;

FIG. 8 is a partial cross-sectional view of the data storage andretrieval device of FIG. 1 during an alignment operation;

FIG. 9 is a partial cross-sectional view of the data storage andretrieval device of FIG. 1 during a blanking/parking operation;

FIG. 10 is a side, cut-away view of the preferred electron emissiondevice;

FIG. 11 is a bottom, cut-away view of the device shown in FIG. 10;

FIG. 12 is a bottom view of the device shown in FIG. 10; and

FIG. 13 is a diagram illustrating an alternative embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawings.

FIG. 1 illustrates an exemplary embodiment of a data storage andretrieval device of the present invention. The data storage andretrieval device includes a control unit 1, a spin-polarized electronsource 40 having a tip 2b, an extractor 4, collimators 6, 7 and 9,electrostatic lenses 10, 11 and 12, and insulating elements 5 and 8. Thedata storage and retrieval device also includes further comprises ablanking element 13, coarse and fine microdeflectors 14 and 15,respectively, an electron detector 16, a data storage layer 17, and asubstrate 18.

The control unit 1, includes a microprocessor or other control circuitryknown in the art. The control unit 1 coordinates and sequences thevarious functions and operations performed by the data storage andretrieval device, as will be explained in more detail below. The controlunit 1 further serves to interface the data storage and retrieval devicewith an external device (not shown), such as a computer or even anotherdata storage and retrieval device, via ADDRESS IN, DATA IN, and DATA OUTterminals. By this interfacing, control signals and data from theexternal device can be transmitted to and decoded by the control unit 1using necessary protocols. The control unit 1 can develop controlresponses and data and return the data to the external device using thenecessary protocols. It is contemplated that the control unit 1 can beinterfaced with the external device via, for example, electrical oroptical links. For instance, optical transmission into and out from thecontrol unit 1 can be accomplished using electrically pumped laserdiodes.

The spin polarized electron source 40, including tip 2b, providesspin-polarized electrons 3. In particular, the spin-polarized electrons3 are developed by the spin polarized electron source 40 and arecollected in the tip 2b. Tip 2b is a modulated self-polarizing sharp tipfor emission of low energy electrons, as described in more detail laterin the application.

Each of the spin-polarized electrons 3 has an electron magnetic fieldwith a direction of polarization determined by the electron's spin. Thedirection of polarization of the electron magnetic field corresponds toone of first and second data values. For example, an upwardly polarizedelectron magnetic field can correspond to a data value of "1" while adownwardly polarized electron magnetic field can correspond to a datavalue of "0", or vice versa.

A potential V₁ is applied to the spin-polarized electron source 40 bythe control unit 1. The strength of the potential V₁ can be varied bythe control unit 1 to control the intensity, which is also known in theart as current, of the spin-polarized electrons 3. A signal S₁₉ is alsoapplied to the spin-polarized electron source 40 by the control unit 1.Signal S₁₉ controls the direction of polarization of the magnetic fieldsof the spin-polarized electrons 3. Preferably, the control unit 1 canvary the potential V₁ and signal S₁₉ during operation of the device tocompensate for factors, such as physical changes in the device and itsenvironment over time, alternative configurations of the device, oralternate media characteristics of the device.

The extractor 4, collimators 6, 7 and 9, electrostatic lenses 10-12, theblanking element 13, and the coarse and fine microdeflectors 14 and 15,respectively, each constitutes, for example, an electrically conductiveannular member defining an aperture. The extractor 4 extracts thespin-polarized electrons 3 from the tip 2b and collimators 6, 7 and 9collimate the spin-polarized electrons 3 into a spin-polarized electronbeam 19. The electrostatic lenses 10-12 focus the spin-polarizedelectron beam 19 and the coarse and fine microdeflectors 14 and 15,respectively, direct the spin-polarized electron beam 19 toward the datastorage layer 17.

The environment through which the spin-polarized electron beam 19travels is preferably an electrically nonconductive and nonionizingenvironment such as a vacuum. It is contemplated, however, that theenvironment through which the spin-polarized electron beam 19 travelscan be any number of other environments known in the art which would notdegrade, but may enhance, passage of the spin-polarized electron beam 19from the electron source 2 to the data storage medium 17.

As shown in FIG. 1, the tip 2b is positioned so as to be perpendicularto the plane of the surface of the extractor 4, at the center of theextractor 4 aperture, and juxtaposed at or near the extractor 4 surface.Preferably, the apertures of extractor 4 and collimator 6 are in theorder of 1 micron and 100 microns in diameter respectively. However,larger or smaller diameters could also be used depending on theparticular design of the data storage and retrieval device and thedesired characteristics of the spin-polarized electron beam 19.

Insulating element 5, which comprises, for example, Si, or the like, ispositioned between the extractor 4 and collimator 6 to separate theirconductive surfaces. Preferably, the diameter of thee aperture ofinsulating element 5 is slightly greater than the diameters of theapertures of extractor 4 and collimator 6 to reduce interaction of theinsulating element 5 with electrostatic fields produced in and electronspassing through the apertures of extractor 4 and collimator 6. One ofordinary skill in the art would now appreciate that the size andconfiguration of extractor 4, collimator 6, and insulating element 5would be driven, in part, by the energy level of the spin-polarizedelectron beam.

Potentials V₂ and V₃ are applied by the control unit 1 to the extractor4 and collimator 6, respectively, to create a magnetic field in theaperture of each. The position of the tip 2b relative to theelectrostatic field produced in the aperture of extractor 4 induce thespin-polarized electrons 3 to jump from the tip 2b and pass through theaperture of extractor 4 to the aperture of collimator 6. Collimator 6focuses the electrons into relatively parallel trajectories toward thedata storage layer. The potentials V₂ and V3 may be adjusted by controlunit 1 to obtain desired characteristics of the spin-polarized electrons3 and the spin-polarized electron beam 19. Control of the potentials V₂and V3 may be performed during operation of the device to compensate forfactors, such as physical changes in the device and its environment overtime, alternative configurations of the device, or alternative mediacharacteristics of the device.

Collimators 7 and 9 and insulating element 8, which can be similar oridentical to extractor 4, collimator 6, and insulating element 5,respectively, constitute an optional lens stage to assist in collimatingthe spin-polarized electrons 3 into the spin-polarized electron beam 19.Collimators 7 and 9 and insulating element 8 can also be used toaccelerate or decelerate the spin-polarized electrons 3 to obtain adesired beam energy.

The potentials V₄ and V₅ can be adjusted by the control unit 1 to obtaindesired characteristics of the spin-polarized electrons 3 and thespin-polarized electron beam 19. Control of the potentials V₄ and V₅ canbe performed during operation of the device to compensate for factorssuch as physical changes in the device and its environment over time,alternative configurations of the device, or alternative mediacharacteristics of the device.

After passing through collimator 9, the spin-polarized electron beam 19passes through electrostatic lenses 10-12. Potentials V₆ -V₈ are appliedto the electrostatic lenses 10-12, respectively, by the control unit 1to create electrostatic fields through the lens apertures. Theseelectrostatic fields focus the spin-polarized electron beam 19 with adesired diameter, e.g., that is to say the desired diameter is, in part,limited by the deBroglie wavelength. The apertures of the electrostaticlenses 10-12 are preferably on the order of 10 to 100 microns indiameter but can be varied depending on the particular design of thedata storage and retrieval device and the desired characteristics, e.g.,intensity, beam shape, type of media targeted, etc., of thespin-polarized electron beam 19. Furthermore, the thicknesses of theelectrostatic lenses 10-12, their relative positions, and the potentialsV₆ -V₈ can be varied to obtain desired characteristics of thespin-polarized electron beam 19. Again, the potentials V₆ -V₈ can bevaried by the control unit 1 during operation of the device tocompensate for factors, such as physical changes in the device and itsenvironment over time, alternative configurations of the device, oralternative media characteristics of the device. Further, theelectrostatic lenses 10-12 can be replaced with fewer or more of suchlenses. One of ordinary skill in the art would now appreciate that thesize and configuration of extractor 4, collimator 6, and insulatingelement 5 would be driven, in part, by the energy level of thespin-polarized electron beam. Also, magnetic lenses can be used in placeof, or in addition to, the electrostatic lenses 10-12, the extractor andthe collimators 6, 7 and 9.

After passing through electrostatic lens 12, the spin-polarized electronbeam 19 passes through the blanking element 13. As will be explained inmore detail below, the blanking element 13 is an optional element whichdisables the effects of the spin-polarized electron beam 19. Thepreferred location of the blanking element 13 is above the coarsemicrodeflector 14, as shown in FIG. 1, to allow the spin-polarizedelectron beam 19 to achieve a steady state.

After passing through the blanking element 13, the spin-polarizedelectron beam 19 passes through the coarse microdeflector 14 and thenthe fine microdeflector 15. Preferably, the coarse microdeflector 14comprises eight poles individually controlled by signals S₂ -S₉ suppliedby the control unit 1. Similarly, the fine microdeflector 14 alsopreferably comprises eight poles individually controlled by signals S₁₀-S₁₇ also supplied by the control unit 1. The coarse and finemicrodeflectors 14 and 15, respectively, direct the spin-polarizedelectron beam 19 toward the data storage layer 17. The electro staticvoltage supplied to each pole in a micro deflector contributes to theelectrostatic field within the deflector. By varying the voltages of thepoles the trajectory of the beam may be changed as it passes through themicro deflector. Of course, as one of skill in the art would understand,the elctrostatic fields do not interact with the spin-polarization ofspin-polarized electron beam 19. Additionally, one of skill in the artwould also understand that magnetic fields are not used to alter thebeam trajectory because they are too large. While the coarsemicrodeflector 14 bends the trajectory of the spin-polarized electronbeam 19 toward a general area on the data storage layer 17, the finemicrodeflector 15 further adjusts the trajectory of the spin-polarizedelectron beam 19 to direct the spin-polarized electron beam 19 at aspecific portion of the data storage layer 17. By gradually bending thespin-polarized electron beam 19 in this manner, distortions andaberrations introduced into the spin-polarized electron beam 19 can bereduced. It is contemplated that the fine microdeflector 15 can enablepositioning of the spin-polarized electron beam 19 to the atomic levelon data storage layer 17. In other words, as manufacturing capabilitiesallow more and more precise fabrication of the materials disclosedherein, it is contemplated that electron beam 19 will be capable ofbeing positioned to effect an area on storage layer 17 as small as thelimit imposed by the deBroglie wavelength of the beam electrons.However, current micro fabrication capabilities limit the single bitstorage area to areas larger than the deBroglie wavelength. Although thecoarse and fine microdeflectors 14 and 15, respectively, have beendescribed to comprise eight poles each, it is contemplated that thecoarse and fine microdeflectors 14 and 15, respectively, can have otherconfigurations known in the art. Further, the relative positions of thecoarse and fine microdeflectors 14 and 15, respectively, and the datastorage layer 17 can be determined as a function of X-Y axes scanningrange of the spin-polarized electron beam 19. Also, magnetic deflectionmay be used in place of, or in addition to, the coarse and fine microdeflectors 14 and 15, respectively. However, electro static deflectionis preferred because of the size of the magnetic field necessary todeflect spin-polarized electron beam 19.

Although not shown in FIG. 1, the data storage and retrieval device canfurther comprise a stigmator element such as that shown in FIG. 2.Preferably, the stigmator element is positioned either between theelectrostatic lens 12 and the blanking element 13 or between theblanking element 13 and the coarse microdeflector 14. As shown in FIG.2, the stigmator element comprises, for example, an electricallyconductive material generating an electrostatic field in the apertureformed by eight stigmator elements 25 individually biased withpotentials V₁₂ -V₁₉. It is contemplated that the stigmator element 25can have other configurations known in the art. The individualpotentials V₁₂ -V₁₉ are applied to the stigmator poles of stigmatorelement 25 by the control unit 1 and are set during operation of thedevice to develop a field that results in a desired shape of thespin-polarized electron beam 19 and to compensate for factors such asphysical changes in the data storage and retrieval device and itsenvironment over time alternative configurations of the device, oralternative media characteristics of the device. Although the stigmatorelement is generally used to provide the spin-polarized electron beam 19with a round cross-sectional shape, the stigmator element can also beused to provide the spin-polarized electron beam 19 with across-sectional shape other than round, e.g. oval.

The electron detector 16 comprises an electrically conductive material,such as a metal, and is configured, for example, as shown in FIG. 1, tooptimize the detection of electrons deflected from or secondaryelectrons emitted by the data storage layer 17. Preferably, the electrondetector 16 is positioned so as not to interfere with the path of thespin-polarized electron beam 19 but close enough to the data storagelayer 17 to detect the deflected or emitted electrons. Electronsstriking the electron detector 16 produce a signal in the electrondetector 16 which is supplied to the control unit 1 as signal S₁₈.

The data storage layer 17 and the substrate 18 together constitute adata storage medium. Preferably, the data storage layer 17 is depositedon the substrate 18 via, for example, sputtering, laser ablation, orother technique known in the art. The substrate 18 comprises a strainlayer 29, a signal routing layer 30, and a non-magnetic andnon-electrically conductive material, such as a glass or ceramic, thatserves as a mechanical support for the data storage layer 17, strainlayer 29, signal routing layer 30.

The data storage layer 17 comprises a fixed number of atomic layers of aferro magnetic material (or equivalent), wherein the fixed number ofatomic layers provides the data storage layer 17 with a magnetic vectoralong perpendicular to its surface, i.e., along its easy magnetic axisis out of plane due to strained interatomic distances imposed by strainlayer 29. For example, in the case where the data storage layer 17comprises Fe, three atomic layers of Fe arranged in a body centeredtetragonal (bct) lattice provide the data storage layer with a strongZ-axis magnetic moment when deposited over a suitable strain layer suchas, for example, Ir. Fe begins to shift, however, to a face centeredcubic (fcc) lattice at numbers of atomic layers greater than three,which causes the magnetic anisotropy of the Fe atoms to shift to the X-Yplane. Similar results can also be achieved by combining Fe with certaindopants or alloying elements, such as Co or Ni or by varying the numberof layers.

Because of the perpendicular magnetic anisotropy of the data storagelayer 17, each lattice of atoms in the data storage layer 17 creates adata magnetic field having a polarization that extends along its easyaxis, i.e., perpendicular to the surface of the data storage layer 17.These data magnetic fields are representatively shown in FIG. 3(a) asdata magnetic fields 23. Like the magnetic fields produced by the spinpolarized electrons 3, each data magnetic field created in the datastorage layer 17 has a direction of polarization corresponding to one offirst and second data values. For instance, an upwardly polarized datamagnetic field can correspond to the data value of "1" while adownwardly polarized data magnetic field can correspond to the datavalue of "0", or vice versa. With this arrangement, portions of the datastorage layer 17 store data in one of two states, i.e., first and seconddirections of magnetic polarity. It is contemplated that these portionsof the data storage layer 17 can be as small as the limit imposed by thedeBroglie wavelength of the beam electrons and the configuration of thedevice, e.g., three atoms wide by three atoms thick.

As shown in FIGS. 4(a) and 4(b), the data storage layer 17 includes aplurality of alignment areas 22 and a parking area 21. Each of thealignment areas 22 and the parking area 21 comprises an electricallyconductive material 27 electrically insulated from the data storagelayer 17 by an insulator 28. The alignment areas 22 and parking area 21are used for performing beam alignment, parking, and blankingoperations, which will be described in more detail below. Potential V₁₀of the parking area 21 and potential V₁₁ of the alignment areas 22 aredetected by the control unit 1, as shown in FIG. 1.

Preferably, the data storage layer 17 has a planar surface. It iscontemplated that the data storage medium can have any number of surfaceshapes, a three dimensional curved surface, to allow all points on thedata storage layer to be approximately equidistant from the center ofthe fine aperture, thereby reducing average electron travel time andproviding a uniform beam depth of focus across the surface of the datastorage layer.

The storing of data in the data storage and retrieval device of FIG. 1is accomplished as follows. Controller 1 receives an address signal anda data-in signal. The spin-polarized electron source 40 provides thespin-polarized electrons 3 with a direction of polarizationcorresponding to one of a first and second data value, depending on thedata-in signal. Next, the extractor 4 extracts the spin-polarizedelectrons 3 from the tip 2b, the collimators 6, 7 and 9 collimate thespin-polarized electrons 3 into the spin-polarized electron beam 19, andthe electrostatic lenses 10-12 focus the spin-polarized electron beam19. A shown in FIG. 5(a), the spin-polarized electron beam 19 isdirected by the microdeflectors 14 and 15 at a data magnetic fieldcreated in the portion of the data storage layer 17 at which data is tobe stored. Controller 1 uses the address signal to determine the portionat which data is to be stored. As shown in FIG. 5(b), upon striking thedata magnetic field with the correct wavelength, the spin-polarizedelectron beam 19 impinges the surface of the data storage layer 17causing a cascading field reversal effect along the easy axis ofmagnetization producing the data magnetic field. As a result, thedirection of polarization of the electrons in the spin-polarizedelectron beam 19 are imparted to the data magnetic field.

To achieve the desired cascading field reversal effect, the wavelengthof the electrons in the spin-polarized electron beam 19 should be set inaccordance with the material used for the data storage layer 17. Inparticular, the wavelength of the spin-polarized electron beam 19 shouldbe approximately equal to the deBroglie wavelength of the electrons inthe outer d subshell of the atoms of the material used for the datastorage layer 17 causing the magnetization vector. In other words, theenergy of the beam should be approximately equal to the kinetic energyof the electrons in the outer d subshell of the atoms of the materialused for the data storage layer 17.

As explained above, it is contemplated that eventually a single datavalue will be stored on a portion of data storage layer 17 as small asthe limit imposed by the deBroglie wavelength of the beam electron;however, current micro fabrication capabilities of data storage layer 17require that the single data value be stored on portions of storagelayer 17 somewhat larger than this minimum limit. However it is alsocontemplated that portions of the data storage layer 17 the multipleatoms wide may also represent a single data value, as shownschematically in FIG. 3(b). If the atoms in the data storage layer 17are grouped as such, the diameter of the spin-polarized electron beamelectron beam 19 should be sized to accommodate the larger data storageareas.

The reading of data from the data storage layer 17 can be accomplishedusing one of two techniques. In the first data reading technique,controller 1 receives an address signal. The spin-polarized electronsource 40 provides the spin-polarized electrons 3 with a direction ofpolarization corresponding to one of a first and second data value.Next, the extractor 4 extracts the spin-polarized electrons 3 from thetip 2b, the collimators 6, 7 and 9 collimate the spin-polarizedelectrons 3 into the spin-polarized electron beam 19, and theelectrostatic lenses 10-12 focus the spin-polarized electron beam 19.The spin-polarized electron beam 19 is then directed by themicrodeflectors 14 and 15 at a portion of the data storage layer 17 fromwhich data is to be read. Controller 1 uses the address signal todetermine the portion at which data is to be read.

As shown in FIG. 6(a), if the direction of polarization of the datamagnetic field of the portion to be read is the same as the direction ofpolarization of the electrons in the spin-polarized electron beam 19,the electrons in the spin-polarized electron beam 19 are attracted bythe data magnetic field and absorbed by the data storage layer 17.Absorption of the electrons by the data storage layer 17 results in thegeneration of a signal S₂₀.

As shown in FIG. 6(b), if the direction of polarization of the datamagnetic field is opposite the direction of polarization of theelectrons in the spin-polarized electron beam 19, the electrons in thespin-polarized electron beam 19 are deflected by the data magnetic fieldand impinge upon the electron detector 16. As previously explained,impingement of the electrons upon the electron detector 16 results inthe generation of the signal S₁₈.

Attraction of the electrons in the spin-polarized electron beam 19 bythe data magnetic field is detected by the control unit 1 as a firstdata value, e.g., a data value of "0", while deflection of the electronsin the spin-polarized electron beam 19 by the data magnetic field isdetected by the control unit 1 as a second data value, e.g., a datavalue of "1". Specifically, the control unit 1 detects and interpretsthe signal S₁₈, the signal S₂₀, or both the signal S₁₈ and the signalS₂₀ at a fixed time relative to the generation of the spin-polarizedelectrons 3 and, therefore, at a fixed time relative to the impact ofthe spin-polarized electron beam 19 with the data storage layer 17. Ifthe signal S₁₈ is not detected and/or the voltage V₂₀ is detected by thecontrol unit 1 a specified time after the generation of thespin-polarized electrons 3, the control unit 1 determines that theelectrons in the spin-polarized electron beam 19 have been attracted bythe data magnetic field and absorbed by the data storage layer 17. Onthe other hand, if the signal S₁₈ is detected and/or the signal S₂₀ isnot detected by the control unit 1 a specified time after the generationof the spin-polarized electrons 3, the control unit 1 determines thatthe electrons in the spin-polarized electron beam 19 have been deflectedby the data magnetic field and detected by the electron detector 16.Preferably, excess electrons in the data storage layer 17 are drained,for example, at the electrode producing signal S₂₀ while excesselectrons in the electron detector 16 are drained, for example, at theelectrode producing the signal S₁₈.

As was the case when storing data, when reading data from the datastorage layer 17 using the first technique, the energy level of thespin-polarized electron beam 19 should be set in accordance with thematerial used for the data storage layer 17. However, when reading datausing the first technique, the energy level of the spin-polarizedelectron beam 19 should be low enough so as not to cause a magneticchange to the data magnetic fields created in the data storage layer 17.

In the second data reading technique, the spin-polarized electron source40 provides the spin-polarized electrons 3 with a direction ofpolarization corresponding to one of a first and second data value.Next, the extractor 4 extracts the spin-polarized electrons 3 from thetip 2b, the collimators 6, 7 and 9 collimate the spin-polarizedelectrons 3 into the spin-polarized electron beam 19, and theelectrostatic lenses 10-12 focus the spin-polarized electron beam 19.The spin-polarized electron beam 19 is then directed by themicrodeflectors 14 and 15 at a portion of the data storage layer 17 fromwhich data is to be read.

In this second technique, the energy of the spin-polarized electron beam19 is at a value higher than that for a data store operation and highenough such that the spin-polarized electron beam 19 penetrates into theportion of the data storage layer 17 causing that portion of the datastorage layer 17 to produce secondary electrons. Preferably, the energyof the spin-polarized electron beam 19 should not be so high as to causethermal migration of the atoms in the lattices of the data storage layer17.

The secondary electrons produced by the data storage layer 17 havespecific energy and spin which are characteristic of the relationshipbetween the direction of polarization of the data magnetic fieldgenerated by the portion of the data storage layer 17 and the directionof polarization of the electrons in the spin-polarized electron beam 19.These secondary electron characteristics are detected as one of thefirst and second data values.

For example, as shown in FIG. 7(a), if the direction of polarization ofthe data magnetic field is the same as the direction of polarization ofthe electrons in the spin-polarized electron beam 19, the data storagelayer 17 produces secondary electrons 24 having a first energy and firstspin characteristics corresponding to the first data value, e.g., a datavalue of "1". Similarly, as shown in FIG. 7(b), if the direction ofpolarization of the data magnetic field is opposite the direction ofpolarization of the electrons in the spin-polarized electron beam 19,the data storage layer 17 produces secondary electrons 26 having asecond energy and second spin characteristics corresponding to thesecond data value, e.g., a data value of "0". The secondary electronsproduced by the data storage layer 17 are detected by the electrondetector 16 to produce signal S₁₈ which indicates the secondary electroncharacteristics. The control unit 1, upon receiving the signal S₁₈,interprets the secondary electron characteristics.

Although this second technique has been described as detecting theenergy and spin characteristics of the secondary electrons produced bythe data storage layer 17, it is contemplated that other characteristicsof the secondary electrons known in the art can be detected to read datastored on the data storage layer 17. Further, although most of thesecondary electrons produced by the data storage layer 17 are emitted bythe data storage layer 17, as shown in FIGS. 7(a) and 7(b), some of thesecondary electrons remain within the data storage layer 17 to producesignal S₂₀. Thus, it is contemplated that the characteristics of thesecondary electrons produced by the data layer 17 can also be detectedand interpreted by the control unit 1 via signal S₂₀.

As shown in FIG. 8, alignment of the spin-polarized electron beam 19 isperformed by directing the beam at one or more of the alignment areas22. When the potential V₁₁ is detected by the control unit 1, theaddressed and targeted alignment areas match. If the potential V₁₁ isnot detected, signals S₂ -S₁₇ to the microdeflectors 14 and 15 can beadjusted by the control unit 1 to compensate for any misalignment.Preferably, alignment of the spin-polarized electron beam 19 occursperiodically during operation of the device. Similarly, the alignmentfunction can be performed by detecting patterns of bits stored atselected locations on the media. Wen the correct pattern has beendetected, addressed and targeted areas match.

As described above, the blanking element 13, under control of thecontrol unit 1, prevents the spin-polarized electron beam 19 fromimpinging the data storage layer 17. The blanking element 13 comprises,for example, two poles controlled with signal S₁. It is contemplatedthat blanking element 13 can have other configurations known in the artand that the poles can be individually controlled. The control unit 1applies the signal S₁ to the blanking element 13 at a specific time andfor a specific duration to blank the spin-polarized electron beam 19while it is being moved by the microdeflectors 14 and 15 to target adifferent portion of the data storage layer 17. The blanking element 13can also be used to blank the spin-polarized electron beam 19 during adata read operation when the control unit 1 is detecting whether or notelectrons are being deflected or emitted by the data storage layer 17.The poles of the blanking element 13 act to diffuse the spin-polarizedelectron beam 19 so the electrons in the beam do not impinge the surfaceof the data storage layer 17 as a beam.

It is contemplated that the microdeflectors 14 and 15 can alternativelybe used to perform blanking of the spin-polarized electron beam 19during data read operations. For example, the control unit 1 can supplythe microdeflectors 14 and 15 with signals S₂ -S₁₇ to cause thespin-polarized electron beam 19 to be directed at a particular area onthe data storage layer 17 that is not used for data storage, e.g.,parking area 21, as shown in FIG. 9. Impingement of the spin-polarizedelectron beam 19 on the parking area 21 is detected as the potential V₁₀by the control unit 1.

Imperfections may exist in the data storage layer 17 as a result offabrication, degradation, or other causes which render one or moreflawed areas of the data storage layer 17 unusable for data storage.Accordingly, a format operation is provided to prevent the reading ofdata from and the storing of data to those flawed areas. For example,during the format operation, the control unit 1 cycles each datamagnetic field created in the data storage layer 17 between up and downpolarities at least once and verifies each result. This format operationcan be performed, for example, by successively using the data read anddata store operations described above. Control unit 1 determines whethercertain portions of the data storage layer 17, from which written datacannot be reliably read, are unusable. Upon completion of the formatoperation, the locations of the unusable portions of the data storagelayer 17 are stored in a memory which is maintained, for example, by thecontrol unit 1 for use in determining where data can be stored duringsubsequent data storage operations.

It is contemplated that the format operation can detect and storelocations of unusable portions of the data storage layer 17 duringoperation of the data storage and retrieval device. For example, aftereach store operation into a portion of the data storage layer 17,control unit 1 could then read from the portion, to verify that theportion is currently non-defective.

The control unit 1 can also use the memory to store locations ofportions of the data storage layer 17 that are used for storing andprotecting data which are read often but stored infrequently. Examplesof this type of data stored in current storage mediums are configurationdata and driver software stored in ROM. This type of data is stored inportions of the data storage layer 17 which are designated protected inthe memory. As an additional precaution to preventing unintentionalchanges to protected data, certain portions of the data storage layer 17can comprise an alternate material for data storage layer 17. Thisalternate material would require a different spin-polarized electronbeam wavelength and/or intensity for storing data than that required byunprotected data locations. Thus, both access to the control unit 1memory and modification of the spin-polarized electron beam wavelengthand/or intensity would be required to change polarities of suchprotected data.

This spin-polarized electron beam has been illustrated with longitudinalspin polarization, however, transverse polarization can also be used.Transverse spin-polarization electron beam polarization requires thatmagnetic moments in the media be in plane and be parallel/antiparallelwith the electron beam polarization and that magnetic coupling betweenstorage areas be insufficient to interfere with beam/mediuminteractions.

An advantage attained by the described method and apparatus iselimination of all moving parts. However, it is contemplated that withthe addition of certain mechanisms, the data storage layer could be madeto move with respect to the beam. This movement could result in rotationof the data storage layer, the exchange of one data storage layer foranother, or other implementations known in the art. Also, the beamformation apparatus can be made to move.

Potentials V₂ -V₈ and V₁₂ -V₁₉ and signals S₂ -S₉, S₁₀ -S₁₇, and S₁₉preferably have adjustable bias components. These bias components areused to compensate for position misalignment, beam deformation, andcorrectable effects to the spin-polarized electron beam 19 caused byother elements. The bias component of an element modifies the effect ofthat element on the spin-polarized electron beam 19 by changing theintensity and shape of the field within the aperture of the element.Preferably, bias adjustments are performed by the control unit 1 duringoperation of the device. They occur in a specific order when the readand write functions are unable to determine or modify the polarity of adata magnetic field created in the data storage layer 17. The amount ofbias compensation for each element is determined by adjustments neededto re-focus the intensity, wavelength, and cross-section of thespin-polarized electron beam 19 on the data storage layer 17 so that aknown data magnetic field can be modified and read.

FIG. 10 shows the electron emission device 40 in more detail.Spin-polarized electron source 40 is a modulated self-polarizing sharptip for emission of longitudinally polarized electrons, electrons havinga spin axis parallel to the emission path. When used with a component,such as extractor 4, the electrons emitted by spin-polarized electronsource 40 have a predominantly similar wavelength. Substrate 2a is forexternal mounting of the tip 2b and is the base component upon whichremaining tip components are fabricated. Substrate 2a includes silicondioxide (SiO₂), or another suitable material, which electricallyseparates magnetizing layer 31 from conducting layer 33 and fromextension 33a, the electrical contact for conducting layer 33.

Insulating layer 32, shown in FIG. 10, is adjacent to magnetizing layer31 and extends past the edge of magnetizing layer 31 near magnetizinglayer extension 31a. Insulating layer 32 includes SiO₂, or anothersuitable material which isolates the currents in magnetizing layer 31and conducting layer 33.

Conducting layer 33 is an ultrathin film ferromagnetic material, such asFe, deposited on insulating layer 32, by molecular beam epitaxy MBE oranother method known in the art. Conducting layer 33 is preferably asingle magnetic domain. Magnetizing layer extension 31a and conductinglayer extension 33a are connected electrically to magnetizing layer 31and conducting layer 33, respectively.

FIG. 11 shows a cut-away view of the electron emission device 40 viewedalong the line 11--11 shown in FIG. 10. (FIG. 10 is a cut-away viewalong the line 10--10 shown in FIG. 11). Magnetizing layer 31 is aconductive metallic material, such as Al, Cu or Au, deposited onsubstrate 2a through a suitable deposition technique. A lithographicprocess, such as MBE or chemical vapor deposition (CVD) may be used toform the layer in any suitable configuration. Magnetizing layer 31includes a series of planar concentric rings with two out-of-planeelectrical contacts for signal voltage S₁₉. However, other suitableconfigurations may also be used.

FIG. 12 shows two electrical connection areas for signal S₁₉ onmagnetizing layer extension 31a, an out-of-plane extension ofmagnetizing layer 31. An electrical connection area for source voltageV₁ is on conducting layer extension 33a, an out-of-plane extension ofconducting layer 33 (See also FIG. 10). Electrical connections aresoldered directly to magnetizing layer extension 31a and conductinglayer extension 33a with indium solder or another suitable materialknown in the art.

The tip 2b is a sharp tip of conducting material that can be grownepitaxially, or by another suitable method known in the art, onconducting layer 33. An integral connection between the tip 2b andconducting layer 33 creates suitable electrical interfacecharacteristics between conducting layer 33 and the tip 2b, reducingelection spin scattering while crossing the interface between layer 33.By controlling the effects of tip 2b and a spin-derived variableimpedance to the flow of spin-polarized electrons into the tip 2b,consistent operational characteristics of the spin-polarized electronsource 40 are better achieved. Thus, more electrons cross the interfacewith their polarization preserved.

No initial or external magnetization of the tip 2b or any other spinpolarized electron source 40 components is required. The signal S₁₉,which is a voltage of alternating [+] or [-] polarity, is connected tothe two electrical connection areas of magnetizing layer extension 31aadjacent to the substrate 2a. A current I₁₉ flows through one electricalconnection area of magnetizing layer 31, through the concentric rings,and out the second electrical connection area of magnetizing layer 31.Current I₁₉ establishes a magnetic field below and above the plane ofthe layer. This generated magnetic field extends perpendicularly throughthe insulating layer 32 and conducting layer 33. Conducting layer 33 ismagnetized in a first direction as a result of the direction of currentI₁₉ flow in magnetizing layer 31. After signal voltage S₁₉ is removed,conducting layer 33 will remain magnetized because it is a paramagneticmaterial. Signal voltage S₁₉ is an alternating polarity voltage that iscontrolled by controller 1 to be in phase with the in-progress deviceoperation. When signal voltage S₁₉ is switched to the opposite polarityby controller 1, conducting layer 33 is magnetized in an opposite orsecond direction. It then remains magnetized in a second direction.Source current I₁ supplied to conducting layer 33 becomes polarized bythe intrinsic magnetization of conducting layer 33 and by the magneticfield established by current I₁₉. The spin polarized current isextracted from the tip 2b at the sharp tip due to penetration of thesharp point of the tip by the electric field gradient from the extractor4 at a point where the curvature of the tip 2b is greatest.

Current carriers in a crystal lattice can be electrons or holes. Thefollowing explanation describes electrons. The 3d subshell of an Fe atomhas 5 electrons of one spin and a sixth electron of opposite spin.Electron spin develops a magnetic moment through intrinsic angularmomentum that is separate from and approximately twice the magnitude oforbital angular momentum. Each electron has a resultant magnetic momentdue to this intrinsic angular momentum. These moments align to form theatomic magnetic moment. The first 5 electrons in the 3d subshell of anFe atom align their spin and resultant magnetic moments with theexternal field developed by magnetizing layer 31 and become parallel toit (within constraints of atomic electron orbital structure and latticestructure). The sixth spin is antiparallel to the first 5, canceling 1electron magnetic moment. Current I₁ includes electrons having randomspin. Therefore, when current flows through a planar thin filmpenetrated perpendicularly by an external magnetic field, electrons inthe current become spin-polarized. As a result, electrons flowingthrough conducting layer 33 are spin-polarized.

The components of the spin-polarized electron source 40 can be in anyconfiguration to generate longitudinally spin-polarized electrons,provided the axis of magnetization through conducting layer 33, whichpolarizes spins, is juxtaposed longitudinally with the emitting surface.Alternatively, generation of transverse polarized electrons can bedeveloped through fabrication of spin-polarized electron source 40components in a configuration modified from the preferred embodiment. Inthis alternative embodiment, the axis of magnetization through aconducting layer is juxtaposed perpendicularly with the emittingsurface.

In general, the spin-polarized electron source can be any source forproviding spin-polarized electrons known in the art. The spin-polarizedelectron source 40 can be used as, for example, the tip of a scanningelectron microscope or other similar device. Preferably, the tip has asmall diameter, such as the diameter of a single atom.

Although a flat data storage layer 17 has been illustrated, it iscontemplated that other shapes and configurations can be used. Forexample, the magnetic media can be segmented into an array of geometricformations such as tiles, cones, pyramids, cylinders, spheres, cubes, orother irregular shapes which may or may not be electrically isolatedfrom each other. The geometric formations may have any shape, providedthe magnetic axis of the electrons in the beam is parallel with themagnetic axis of the illuminated atoms in the geometric formation.

FIG. 13 shows a portion of an alternative embodiment of the presentinvention. Cylinders 35 include a ferromagnetic material on a substrate34. The easy magnetic axis of cylinders 35 can be longitudinal. Thiseasy magnetic axis is oriented parallel with longitudinally spinpolarized electrons in the beam 19 in order to polarize the magneticaxis of the cylinders 35.

As another alternative, the magnetic media could be cone-shapedformations deposited in a regular array on a surface. A magnetic axis ofthe cones could be parallel with the plane of the surface, requiringspin-polarized electrons that are transversely polarized in the beam topolarize the magnetic axis of the cones.

Although an Fe magnetic media has been illustrated, anymultiple-electron metal with co-mingling ranges of binding energies of for s subshell electrons with that of an outer d subshell and which canbe made to exhibit ferromagnetism via a strained lattice structure, suchas bct, in few atomic layers can be used as the magnetic media.Candidate metals for the magnetic media can be from the three periodictable transition series. For example, candidate metals from the 3dseries can include Co and Ni. Similarly, candidate metals from the 4dand 5d series can include Mo and Ir, respectively. These metals functionin a manner similar to a Fe magnetic media previously described on pages14 through 17.

Although the above disclosure is directed to a single electron beam itwould be apparent to one of ordinary skill in the art that multipleelectron beams could be incorporated into the device. In thisalternative, the electron beam and the spin-polarized electrons would bedirected at multiple portions of the member that correspond to theaddress signals transmitted to a control unit. Thus, devices consistentwith the present invention would be capable of controlling thewavelength of multiple beam electrons such that multiple portions of amagnetic storage layer assume magnetic polarizations corresponding tothe magnetic polarization of the beam electrons directed at thatportion. The control unit would also include means responsive to addresssignals, for detecting the polarizations of multiple portions of thedata storage layer corresponding to the address signals, by directingthe beams at the multiple portions.

It should be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A data storage device comprising:a memberincluding a magnetic material; and means for generating a beam ofelectrons, said beam of electrons having a common polarization, saidbeam being directed at select portions of said magnetic material;wherein said beam of electrons interacts with select portions of saidmagnetic material to polarize said select portions of said magneticmaterial to at least one of a plurality of discrete orientations.
 2. Thedata storage device recited in claim 1, wherein said magnetic materialhas a fixed number of atomic layers having a magnetic anistropy.
 3. Thedata storage device recited in claim 1, wherein said beam of electronshas a wavelength approximately equal to the deBroglie wavelength of theelectrons in an outer d subshell of the atoms of said magnetic material.4. The data storage device recited in claim 1, wherein said magneticmaterial contains Fe arranged in a body centered tetragonal latticehaving an average thickness of three atoms.
 5. A data retrieval devicecomprising:a member including a magnetic material, said magneticmaterial having select portions with at least two discretepolarizations; means for generating a beam of electrons, said beam ofelectrons having a common polarization, said beam being directed atselect portions of said magnetic material; and means for detectingreflected electrons from said beam of electrons wherein said beam ofelectrons interacts with said select portions of said magnetic materialand is absorbed if said common polarization of said electrons is thesame as said magnetic material or is reflected if said commonpolarization is said electrons is different than said magnetic material.6. The data retrieval device recited in claim 5, wherein said magneticmaterial has a fixed number of atomic layers having a magneticanistropy.
 7. The data retrieval device recited in claim 5, wherein saidmagnetic material contains Fe arranged in an body centered tetragonallattice having an average thickness of three atoms.
 8. The dataretrieval device comprising:a member including a magnetic material, saidmagnetic material having select portions with at least two descretepolarizations; means for generating a beam of electrons, said beam ofelectrons having a common polarization, said beam being directed atselect portions of said magnetic material; and means for detectingreflected electrons from said beam of electrons wherein said beam ofelectrons interacts with select portions of said magnetic material andis modified to create reflected electrons, said reflected electronshaving either a first spin characteristic or a second spincharacteristic depending upon the magnetic polarization of said magneticmaterial in said select portion.
 9. A data retrieval device recited inclaim 8, wherein said magnetic material has a fixed number of atomiclayers having a magnetic anistropy.
 10. The data retrieval devicerecited in claim 8, wherein said magnetic material contains Fe arrangedin a body centered tetragonal lattice having an average thickness ofthree atoms.